Andrzej Duda was forced to correct Mr Trump during a joint press conference as part of the US leader’s second foreign visit.

The former real estate mogul joked that the US would be able to influence the pricing for Liquid Natural Gas (LNG) exports.

“Maybe we can get your price up a little bit, but that's okay. He's a tough negotiator,” he said.

“We can enter a contract within the next 15 minutes. Do you have anybody available to negotiate?”

But Mr Duda reminded Mr Trump that imports are private transactions and are not negotiated between governments.

“It is not the president of the United States and the president of Poland who are going to sign the long-term contract for LNG gas deliveries to Poland,” he said. “But the contract will be signed by companies, by a Polish company and an American company.”

Poland began receiving shipments of US LNG earlier in the year.

While the US approves permits that allow export terminals to operate, LNG purchases are private transactions.

It came after Mr Trump pledged stronger trade ties between Poland and the US.

"America stands ready to help Poland and other European nations diversify their energy supplies, so that you can never be held hostage to a single supplier," he said.

European Council President Donald Tusk said he welcomed the “surprising diplomatic words” from Mr Trump during the meeting in Warsaw.

Mr Trump said he stood firmly behind the mutual defence commitments of the Nato alliance and criticised Russia in the meeting ahead of the G20 summit.

Mr Tusk, a former Polish prime minister who has voiced concern at Mr Trump's apparent willingness to favour better ties with Moscow at the expense of the EU, said: "I've heard yesterday in Warsaw, surprising diplomatic words from the American president about Transatlantic community, about the cooperation between the United States, Europe, about our common political tradition and civilisation, and about the readiness to protect and to defend the whole Western community.

"We have been waiting for a long time to hear these words from President Trump but the real question is whether it was a one-time incident or a new policy."